Miao RM, Zhang XT, Guo P, He EQ, Zhou F, Zhao DK, Zhang YY. Effect of oxidative stress on development of silicosis. World J Respirol 2012; 2(1): 1-5 [DOI: 10.5320/wjr.v2.i1.1]
Corresponding Author of This Article
Rong-Ming Miao, MD, Department of Occupational Disease, Wuxi Hospital for Prevention and Treatment of Occupational Disease, 93 Xishi Road, Wuxi 214028, Jiangsu Province, China. fang3211010@yahoo.com.cn
Article-Type of This Article
Brief Article
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Rong-Ming Miao, Ping Guo, Fang Zhou, Dao-Kun Zhao, Ying-Yi Zhang, Department of Occupational Disease, Wuxi Hospital for Prevention and Treatment of Occupational Disease, Wuxi 214028, Jiangsu Province, China
Xue-Tao Zhang, Department of Occupational Disease, Yangpu District Central Hospital, Shanghai 200082, China
En-Qi He, Wuxi Center for Disease Control and Prevention, Wuxi 214023, Jiangsu Province, China
ORCID number: $[AuthorORCIDs]
Author contributions: Miao RM and Zhang XT contributed equally to this work; Miao RM, Zhang XT and He EQ designed research; Miao RM, Guo P, Zhou F and Zhao DK performed research; Miao RM, Zhang XT and Zhao DK analyzed data; and Miao RM, Zhang XT and Zhang YY wrote the paper.
Correspondence to: Rong-Ming Miao, MD, Department of Occupational Disease, Wuxi Hospital for Prevention and Treatment of Occupational Disease, 93 Xishi Road, Wuxi 214028, Jiangsu Province, China. fang3211010@yahoo.com.cn
Telephone: +86-510-82726712 Fax: +86-510-82726712
Received: December 10, 2011 Revised: February 10, 2012 Accepted: February 18, 2012 Published online: February 28, 2012
Abstract
AIM: To investigate the changes of oxidative stress indicators in the serum of silicosis patients and explore the mechanism of silicosis development.
METHODS: Two hundred workers who were exposed to silica dust for more than one year were recruited as dust-exposed group, 100 non-dust-exposed subjects served as control group, 32 patients with suspected 0+ silicosis as observation group, and 130 silicosis patients were taken as the silicosis group. Indicators of oxidative stress, including superoxide dismutase (SOD), nitric oxide (NO), serum glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), nitric oxide synthase (NOS), and lipid malondialdehyde (MDA), were determined in all the groups.
RESULTS: Compared with the control group, NO and GSH-Px in dust-exposed group and silicosis group increased, and SOD decreased significantly (81.162 ± 35.176, 270.469 ± 39.228 and 68.209 ± 21.528, respectively, P = 0.004, P = 0.002, P = 0.005). Compared with the control and dust-exposed group, T-AOC, NOS and MDA in silicosis group increased significantly (13.048 ± 4.153, 36.201 ± 7.782 and 5.054 ± 1.204, respectively, P = 0.018, P = 0.022, P = 0.011). Compared with dust-exposed group, GSH-Px in the silicosis group increased significantly (270.469 ± 39.228, P = 0.002). GSH-Px in phase III silicosis was significantly higher than in phase I silicosis (290.750 ± 39.129, P = 0.021). Pearson correlation analysis showed that serum GSH-Px was positively correlated with silicosis staging, length of dust exposure and type of occupation (47.109 ± 8.015, P = 0.001).
CONCLUSION: The imbalance of oxidative and anti-oxidation system is associated with the development of silicosis. The surveillance of oxidative stress indicators will benefit the prognosis of silicosis patients.
Citation: Miao RM, Zhang XT, Guo P, He EQ, Zhou F, Zhao DK, Zhang YY. Effect of oxidative stress on development of silicosis. World J Respirol 2012; 2(1): 1-5
Silicosis is the most destructive form of pneumoconiosis caused by the inhalation of SiO2. Exposure to silica particles smaller than 10 micrometers is considered a major cause of silicosis. According to the United States National Institute for Occupational Safety and Health, the most important factor in the development of silicosis is “the product of the concentrations of dust containing respirable silica in workplace air and the percentage of respirable silica in the total dust[1]. The disease is associated with inflammation of the respiratory system that eventually results in fibrosis, the hardening of the lungs, reducing the ability of the patients to breathe efficiently[2].The pathological manifestation includes macrophages alveolitis, silicotic nodule and dust fibration[3]. The role of macrophages has been investigated[4], but the pathogenesis remains unclear. The imbalance of oxidation and anti-oxidation due to long-term exposure to silica dusts may be one of the causative factors for silicosis[5]. This study aims at clarifying the pathogenesis of silicosis by observing oxidative stress indicators in peripheral blood of silicosis patients in an attempt to search for new strategies for the prevention and treatment of silicosis.
MATERIALS AND METHODS
Subjects
This research was approved by the Ethics Committee of Wuxi Hospital for Prevention and Treatment of Occupational Disease, Wuxi, China. All subjects were male and they were divided into control group, dust-exposed group, and silicosis patient group. The control group was composed of hotel staff who had no silica dust exposure (age 48.7± 8.0 years, n = 100). The dust-exposed group consisted of workers from a local casting factory who had more than one year dust-exposure (age 50.78 ± 9.4 years, n = 200). The silicosis patient group was composed of in-patients and out-patients who have been admitted to our hospital since 2008 (age 52.0 ± 10.4 years, n = 130). There were 64 phase I, 46 phase II, and 20 phase III silicosis patients in this group. Besides, the cases of suspected 0+ silicosis were chosen as observation group (age 53.0 ± 9.12 years, n = 32). There was no significant difference in the age among the groups (P > 0.05). None of the subjects had working experience with radiation and toxic substance, and digestive disorders. No one had taken anti-oxidants, such as Vitamin C, Ginggo leaf or Teapol, one month before the test.
Methods
A questionnaire was designed and used to collect the general information of the subjects, including age, history of dust exposure and smoking, and past and family histories[6]. Physical examination, electrocardiogram, high-kilovolt X-ray, pulmonary function tests including forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC and maximal voluntary ventilation, and abdominal ultrasonography were performed and serum fasting glucose, lipids, liver and kidney functions were examined.
Silicosis diagnosis
All the subjects were diagnosed and categorized based on the “Diagnostic Criteria of Pneumoconiosis”[7].
Blood sample collection
Five milliliter peripheral blood was taken before breakfast, then centrifuged and preserved under -80 °C.
Reagents and instruments
Superoxide dismutase (SOD), nitric oxide (NO) enzyme-linked immunosorbent assay kit (Biosource Corporation, United States). Serum glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), nitric oxide synthase (NOS), malondialdehyde (MDA) test kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China), automatic biochemical analyzer (Beckman Inc., United States), Spiro lab II portable spirometer (MIR Company, Italia), 550 microplate reader (BIORAD, United States), and New Century T6 ultraviolet (UV)-visible spectrophotometer (Beijing Puxi General, Beijing, China).
Test of oxidative stress indicators
SOD activity and NO levels were detected by enzyme-linked immunosorbent assay. GSH-Px activity, T-AOC and NOS were detected by chemical colorimetric assay. MDA was detected by dithiobisnitro-benzoate colorimetric assay and UV spectrophotometer was used for colorimetric assay. All the detections were performed manually according to the manufacturers’ instructions.
Statistical analysis
All the data were expressed as mean ± SD. SPSS11.5 was used for statistical analysis. Univariate analysis of variance and Pearson correlation analysis were used for the significance comparison between each group. P < 0.05 was considered statistically significant.
RESULTS
Comparison of general indicators between each group
There was no significant difference in the blood pressure, blood glucose, blood lipids, creatinine, urea nitrogen, and alanine aminotransferase between groups (P > 0.05) (Table 1).
Table 1 Comparison of general indicators between control group, dust-exposed group and silicosis patient group.
Group
n
Age (yr)
Systolic pressure (mmHg)
Diastolic pressure (mmHg)
Blood glucose (mmol/L)
Triglyceride (mmol/L)
Cholesterol (mmol/L)
Creatinine (μmol/L)
Urea nitrogen (mmol/L)
Alanine transarninase (mmol/L)
Control
100
48.7 ± 8.0
130.42 ± 8.65
82.65 ± 7.68
4.93 ± 0.94
1.45 ± 0.94
5.15 ± 1.03
71.80 ± 16.50
5.53 ± 1.20
24.31 ± 17.44
Dust-exposed
200
50.8 ± 9.4
129.53 ± 9.45
84.72 ± 8.96
4.95 ± 0.79
1.52 ± 0.42
4.24 ± 0.89
69.97 ± 18.96
6.37 ± 1.16
29.16 ± 16.68
Silicosis
130
52.0 ± 10.4
131.42 ± 10.23
84.52 ± 8.14
5.06 ± 0.94
1.53 ± 0.90
4.75 ± 0.92
80.12 ± 19.10
6.47 ± 1.87
27.10 ± 16.83
Comparison of serum NO, SOD, MDA, T-AOC, NOS and GSH-Px between each group
NO in dust-exposed and silicosis groups was significantly higher than in the control group (P < 0.01), while there was no difference between dust-exposed group and silicosis patient group (P > 0.05). SOD in dust-exposed and silicosis group was lower than in the control group (P < 0.01), whereas there was no difference between silicosis and dust-exposed group (P > 0.05). T-AOC, NOS and MDA in silicosis group were obviously higher than in the control group and dust-exposed group (P < 0.05, P < 0.01), but there was no difference between the control group and dust-exposed group (P > 0.05). GSH-Px in dust-exposed group and silicosis group was higher (P < 0.05, P < 0.01) than in the control group, but it was even higher in silicosis group, and the difference was statistically significant (P < 0.01) (Table 2).
Table 2 Comparison of nitric oxide, superoxide dismutase, malondialdehyde, total antioxidant capacity, nitric oxide synthase and serum glutathione peroxidase between control, dust-exposed group and silicosis patient group.
Comparison of NO, SOD, MDA, T-AOC, NOS and GSH-Px between observation group and silicosis group at different stages
Compared with observation group and phase I silicosis, GSH-Px in phase III silicosis increased, and the difference was statistically significant (P <0.05). There was no significant difference in the NO, SOD, MDA, T-AOC, NOS and GSH-PX between observation group and different stages of silicosis (P > 0.05) (Table 3).
Table 3 Comparison of nitric oxide, superoxide dismutase, malondialdehyde, total antioxidant capacity, nitric oxide synthase and serum glutathione peroxidase between observation group and silicosis at different stages.
Serum GSH-Px was positively correlated with the silicosis stage, category, length of dust exposure and type of occupation (based on the exposure concentration of dust), and the differences were statistically significant (P < 0.01) (Table 4).
Pathogenesis of silicosis mainly involves oxidative stress, cytokines, cell apoptosis and immunity doctrine[8-12]. Although the pathogenesis varies, the mechanism that the SiO2 stimulates the body to secrete a variety of cytokines and other biological activity substances resulting in the fibrosis of lung tissue, is affirmative[13-16]. The clinical diagnosis of silicosis rely mainly on the chest radiograph, but a definite diagnosis is often established when the lesion is irreversible, imposing heavy economic burdens on both the patient and society[17,18]. If the quantitative and qualitative changes of these cytokines can be detected earlier and one or more cytokines as a relatively specific indicator can be found, it will be of great significance for the early diagnosis of silicosis and the dust-exposed population census. Many early stage biomarkers have been found in the sera of human and animals. Reactive oxygen species/reactive nitrogen species (ROS/RNS)[5,19], cytokines[20,21] and apoptosis-related factors[22] are indicators related to the early biological indicators of silicosis. Clara cell protein CC16[23,24], the lung surface active substances D and heme monooxygenase-1 are early specific indicators for silicosis[23,25,26]. With the progress made in the pathogenesis studies of silicosis, a variety of theories have become available. Free radical is one of the most important theories. Under physiological circumstances, the normal metabolic process continuously generates free radicals meanwhile they are eliminated by the antioxidant mechanisms in order to maintain homeostasis. When the body is subjected to different kinds of harmful stimuli, oxidative stress occurs and more bioactive molecules such as ROS and RNS are produced that exceeds the removal of oxide, resulting in the imbalance of oxidation and anti-oxidation system[27,28]. This research shows that the imbalance of oxidation and anti-oxidation system existed in both the dust-exposed group and silicosis group, which was particularly remarkable in silicosis group. The increase of NO, NOS, T-AOC and MDA and the decrease of SOD are the prime manifestations. It suggests that silica dust can induce the occurrence of oxidative stress and increase lipid peroxidation, and then cause lung tissue damage. Since serum GSH-Px increases with stages of silicosis, it may be related to the severity of silicosis. Silicosis patients have a higher level of oxidant and anti-oxidant molecules. It may be caused by the continuous production of free radicals and lipid peroxidation with the development of silicosis[29,30]. As the illness progresses, oxidative stress becomes more severe. Therefore, the abnormality of oxidative stress indicators not only suggests the existence of silicosis, but also the inevitable outcome of silicosis. These indicators can be used to predict the occurrence, development, severity and prognosis of silicosis in clinical practice. Due to the known effects of oxidative damage in the development of silicosis, administration of antioxidant agents is a potential strategy for the prevention and treatment of silicosis.
COMMENTS
Background
Silicosis is the most destructive form of pneumoconiosis caused by the inhalation of SiO2.The pathological manifestation includes macrophages alveolitis, silicotic nodule and dust fibration. But the pathogenesis is still unclear.
Research frontiers
The imbalance of oxidation and anti-oxidation induced by long-term exposure to silica dusts may be one of the causes for silicosis. The authors investigated the pathogenesis of silicosis by observing oxidative stress indicators in the peripheral blood of silicosis patients in an effort to search for new therapies for the disease.
Innovations and breakthroughs
The authors concluded that the imbalance of oxidation and anti-oxidation system exists in both the dust-exposed group and silicosis group, particularly evident in silicosis group. As the illness progresses, the oxidative stress becomes more severe. So, the abnormality of oxidative stress indicators suggests not only the existence of silicosis, but also the inevitable outcome of silicosis.
Applications
The oxidative stress indicators can be used to predict the occurrence, development, severity and prognosis of silicosis in clinical practice. Due to the important effects of oxidative damage in the development of silicosis, administration of antioxidant agents will be a potential strategy for the prevention and treatment of silicosis.
Terminology
Silicosis is the most destructive form of pneumoconiosis caused by the inhalation of SiO2. When the body is subjected to different kinds of harmful stimuli, oxidative stress occurs and more bioactive molecules such as reactive oxygen species and reactive nitrogen species will be produced that exceeds the removal of oxide, resulting in the imbalance of oxidation and anti-oxidation system.
Peer review
The paper is a short epidemiological study about oxidative stress occurrence in healthy and dust-exposed subjects and silicosis patients and addresses an important issue about the plasma level of oxidative stress-related molecules and its correlation with silicosis.
Footnotes
Peer reviewer: Vinit Stéphane, PhD, Research Associate, Spinal Cord Injury and Respiratory Physiology Research Group, Department of Comparative Biosciences, School of Veterinary Medicine, The University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, United States
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